Carbon-silicon three-dimensional structural composite material and preparation method thereof

ABSTRACT

Provided are a carbon-silicon three-dimensional structural composite material and a preparation method thereof. The preparation method includes: dissolving graphene quantum dots in ultrapure water, dropwise adding a CuCl 2  or ZnCl 2  solution, and performing oscillation to generate a mixed emulsifier; mixing the mixed emulsifier with a graphite oxide aqueous solution and a cyclohexane solution containing nanosilicon spheres, and performing homogenization to form a uniform oil-in-water emulsion; adding hydrazine hydrate into the obtained emulsion for reduction, and performing a hydrothermal reaction to obtain a reduced emulsion; and freeze-drying the reduced emulsion, performing washing with a washing liquid, and performing vacuum drying to obtain a carbon-silicon three-dimensional structural composite material

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 17/875,611, filed on Jul. 28, 2022, which claims priority toChinese Patent Application No. 202110863229.8, filed on Jul. 29, 2021.The afore-mentioned patent applications are hereby incorporated byreference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the field of electrode materials, inparticular to a carbon-silicon three-dimensional structural compositematerial and a preparation method thereof.

BACKGROUND

A silicon material is considered as the most promising next-generationelectrode material because of its high capacity. However, during theprocess of charging and discharging, the volume of silicon changesgreatly, which leads to cracking and collapse of the electrode materialstructure; and an SEI film on the surface of the material has a sidereaction with an electrolyte at the same time, resulting in decrease ofcapacity and service life, etc. At present, an existing improvementtechnology lies in that silicon-carbon composite materials are preparedto reduce volume expansion of silicon and to reduce the loss of thematerial capacity.

Chinese invention patent with the Application No. CN201010256875.Xdiscloses a graphene/silicon lithium-ion battery negative electrodematerial and a preparation method thereof. According to this preparationmethod, self-supporting graphene/silicon composite film materials withdifferent proportions can be prepared by mixing graphene oxide withnanosilicon powder in different proportions, performing ultrasonicdispersion, performing suction filtering or direct drying to obtaincakes/films, and baking them in a reducing atmosphere. Although thispreparation method can alleviate the volume expansion caused by thesilicon material to a certain extent, an overall specific capacity ofthe material is low. In an existing preparation method of asilicon-carbon composite material, a silicon material and a carbonmaterial are assembled or mixed to relieve the volume expansion of thesilicon material and improve the gram capacity of the material. However,compounding on the surface will hinder conduction of electrons and ions,increase polarization of charging and discharging, and then affect acycle life and rate performance of the material.

SUMMARY

The purpose of the present disclosure is to provide a carbon-siliconthree-dimensional structure composite material and a preparation methodthereof, which solve the problems of volume expansion of a siliconmaterial and cracking and collapse of an electrode material structure.

The present disclosure is realized by the following technical solutions:

A preparation method of a carbon-silicon three-dimensional structuralcomposite material includes the following steps:

-   -   a first step of dissolving 0.004 g to 0.006 g of graphene        quantum dots in 4 ml to 6 ml of ultrapure water, dropwise adding        0.65 ml to 0.85 ml of a CuCl₂ or ZnCl₂ solution having a        concentration of 0.2 mol/ml to 0.3 mol/ml, and performing        oscillation to generate a mixed emulsifier;    -   a second step of mixing the mixed emulsifier obtained in the        first step with 10 ml to 20 ml of a graphite oxide aqueous        solution having a concentration of 10 mg/ml to 20 mg/ml and 10        ml to 20 ml of a cyclohexane solution containing 0.1 g to 0.2 g        of nanosilicon spheres, and performing homogenization for 20 s        to 30 s to form a uniform oil-in-water emulsion;    -   a third step of adding 0.9 g to 1.2 g of hydrazine hydrate into        the emulsion obtained in the second step for reduction, and        performing a hydrothermal reaction to obtain a reduced emulsion;        and    -   a fourth step of freeze-drying the reduced emulsion obtained in        the third step, and performing washing with a washing liquid,        and performing vacuum drying, to obtain the carbon-silicon        three-dimensional structural composite material.

According to the technical solution of the present disclosure, thegraphene quantum dots are utilized with their surface activity for thefirst time to be mixed and react with transition metal chloride toprepare an emulsifier; the prepared mixed emulsifier plays anemulsifying role in the reaction between the graphite oxide aqueoussolution and the nanosilicon sphere solution; the graphite oxide(graphene oxide) is reduced into graphene by using a reducing agent, andenters an oil phase from the aqueous phase; while the graphite oxide isbeing reduced, the silicon spheres are wrapped, so that the siliconspheres are embedded between the layers of the graphene, therebyobtaining the carbon-silicon three-dimensional structural compositematerial.

In some embodiments, the graphene quantum dots in the first step areprepared by: uniformly dissolving 1 g of citric acid and 0.03 g ofhistidine in 20 ml of ultrapure water under a heating condition of a 40°C. to 50° C. water bath, performing pyrolysis at 180° C. for 3 h to forma mixture, filtering the mixture, pouring a filtrate in a dialysis bagfor dialysis treatment, and performing freeze-drying at −40° C. afterthe dialysis treatment to obtain the graphene quantum dots.

The graphene quantum dots of the present disclosure are prepared by ahydrothermal method, which is simple in process and suitable forlarge-scale industrial application.

In some embodiments, the graphite oxide in the second step is preparedby a Hummer method.

In some embodiments, the nanosilicon spheres in the second step have aparticle diameter denoted by r, where r satisfies 20 nm≤r≤120 nm.

In some embodiments, the cyclohexane solution containing the nanosiliconspheres in the second step is prepared by: adding the nanosiliconspheres into a mixed solution prepared by acetone, ethanol, and wateraccording to a volume ratio of 1:1:1, performing ultrasonic treatmentfor 30 min, performing washing with ethanol and ultrapure water forthree times after the ultrasonic treatment, performing centrifugalseparation, taking a lower layer of solid, performing vacuum drying at60° C. to obtain treated nanosilicon spheres, and uniformly dispersing0.1 g to 0.2 g of the treated nanosilicon spheres in 10 ml to 20 ml of acyclohexane solution.

In some embodiments, the hydrothermal reaction in the third step isperformed at a temperature of 60° C. to 65° C. for 8 h to 10 h.

In some embodiments, the freeze-drying in the fourth step is performedat a temperature of −40° C.

In some embodiments, the washing liquid in the fourth step is ethanol.

In some embodiments, the vacuum drying in the fourth step is performedat a temperature of 60° C.

The present disclosure further provides a carbon-siliconthree-dimensional structural composite material obtained by the abovepreparation method of the carbon-silicon three-dimensional structuralcomposite material; and an overall size of the obtained carbon-siliconcomposite material obtained through the wrapping is 3 μm to 10 μm.

Compared with the related art, the present disclosure has the followingadvantages and beneficial effects:

According to the present disclosure, the outside of a silicon materialis wrapped with a carbon material, so that the silicon spheres areembedded between the layers of the carbon material; when the volume ofthe silicon material changes drastically, good elasticity and dispersedstress of the three-dimensional network structure can effectivelyrelieve the material cracking caused by volume expansion, reduce theloss of active materials, avoid side reactions, reduce consumption ofactive lithium ions in an electrolyte, and thus improve a cycle life ofthe material.

Meanwhile, the network structure increases electron transport channels,strengthens electrical connection between the silicon materials,increases an electrical transmission rate, improves conductivity of thematerial itself, and improves the rate performance of the material.

BRIEF DESCRIPTION OF DRAWINGS

The drawings illustrated here are used to provide a furtherunderstanding of embodiments of the present disclosure, and form a partof the present disclosure, but do not constitute a limitation on theembodiments of the present disclosure.

FIG. 1 is an SEM diagram of a carbon-silicon three-dimensionalstructural composite material prepared in Embodiment 2, in which a showsan overall morphology of the carbon-silicon composite material; and bshows a morphology of a surface, which is wrapped by graphene, of thecarbon-silicon composite material.

FIG. 2 shows comparison of electrode material specific capacities of acarbon-silicon three-dimensional structural composite material preparedin Embodiment 2 and an existing pure silicon material at differentcurrent densities, in which c shows the carbon-silicon three-dimensionalstructural composite material of the present disclosure; and d shows apure silicon material electrode.

DESCRIPTION OF EMBODIMENTS

In order to make the purpose, technical solution and advantages of thepresent disclosure clearer, the present disclosure will be described infurther detail below with reference to embodiments and drawings.Illustrative implementations of the present disclosure and descriptionsthereof are only used to explain the present disclosure, but not tolimit the present disclosure.

Embodiment 1

Material Preparation:

-   -   a. nanosilicon sphere treatment: the particle diameter r of        nanosilicon spheres was 20 nm; the nanosilicon spheres were        added into a mixed solution prepared by acetone, ethanol and        water according to a volume ratio of 1:1:1; washing was        performed with ethanol and ultrapure water for three times after        ultrasonic treatment for 30 min; centrifugal separation was        performed to take the lower layer of solid; vacuum drying was        performed at 60° C. to obtain treated nanosilicon spheres; and        0.1 g of the treated nanosilicon spheres was uniformly dispersed        in 10 ml of a cyclohexane solution;    -   b. 1 g of citric acid and 0.03 g of histidine were uniformly        dissolved in 20 ml of ultrapure water under a heating condition        of a 40 to 50° C. water bath; pyrolysis was performed at 180° C.        for 3 h to form a mixture; the mixture was filtered; a filtrate        was poured in a dialysis bag for dialysis treatment; and        freeze-drying was performed at −40° C. after the dialysis        treatment to obtain graphene quantum dots;    -   c. graphite oxide was prepared by a Hummer method; and the        concentration of a graphite oxide aqueous solution was 10 mg/ml.

Preparation Steps:

-   -   uniformly dissolving 0.004 g of the graphene quantum dots in 4        ml of ultrapure water, dropwise adding 0.65 ml of a 0.2 mol/ml        CuCl₂ solution, and performing oscillation to generate a mixed        emulsifier;    -   mixing the obtained mixed emulsifier with 10 ml of the graphite        oxide aqueous solution having a concentration of 10 mg/ml and 10        ml of the cyclohexane solution containing 0.1 g of the        nanosilicon spheres, and performing homogenization for 20 s to        form a uniform oil-in-water emulsion;    -   adding 0.9 g of hydrazine hydrate into the obtained emulsion in        three times for reduction; and performing a hydrothermal        reaction at 60° C. for 8 h to obtain a reduced emulsion;    -   freeze-drying the obtained reduced emulsion at −40° C.,        performing washing with ethanol for three times, and performing        vacuum drying at 60° C. to obtain a carbon-silicon        three-dimensional structural composite material.

Embodiment 2

Material Preparation:

-   -   a. nanosilicon sphere treatment: the particle diameter r of        nanosilicon spheres was 50 nm; the nanosilicon spheres were        added into a mixed solution prepared by acetone, ethanol and        water according to a volume ratio of 1:1:1; washing was        performed with ethanol and ultrapure water for three times after        ultrasonic treatment for 30 min; centrifugal separation was        performed to take the lower layer of solid; vacuum drying was        performed at 60° C. to obtain treated nanosilicon spheres; and        0.15 g of the treated nanosilicon spheres was uniformly        dispersed in 15 ml of a cyclohexane solution;    -   b. 1 g of citric acid and 0.03 g of histidine were uniformly        dissolved in 20 ml of ultrapure water under a heating condition        of a 45° C. water bath; pyrolysis was performed at 180° C. for 3        h to form a mixture; the mixture was filtered; a filtrate was        poured in a dialysis bag for dialysis treatment; and        freeze-drying was performed at −40° C. after the dialysis        treatment to obtain graphene quantum dots;    -   c. graphite oxide was prepared by a Hummer method; and the        concentration of a graphite oxide aqueous solution was 15 mg/ml.

Preparation Steps:

-   -   uniformly dissolving 0.005 g of the graphene quantum dots in 4        to 6 ml of ultrapure water, dropwise adding 0.75 ml of 0.25        mol/ml CuCl₂ solution, and performing oscillation to generate a        mixed emulsifier;    -   mixing the obtained mixed emulsifier with 15 ml of the graphite        oxide aqueous solution with a concentration of 15 mg/ml and 15        ml of cyclohexane solution containing 0.15 g of nanosilicon        spheres, and performing homogenization on the obtained mixture        for 25 s to form a uniform oil-in-water emulsion;    -   adding 0.9 g of hydrazine hydrate into the obtained emulsion in        three times for reduction, and performing a hydrothermal        reaction at 63° C. for 9 h to obtain a reduced emulsion; and    -   freeze-drying the obtained reduced emulsion at −40° C.,        performing washing with ethanol for three times, and performing        vacuum drying at 60° C. to obtain a carbon-silicon        three-dimensional structural composite material.

Embodiment 3

Material Preparation:

-   -   a. nanosilicon sphere treatment: the particle diameter r of        nanosilicon spheres was 120 nm; the nanosilicon spheres were        added into a mixed solution prepared by acetone, ethanol and        water according to a volume ratio of 1:1:1; washing was        performed with ethanol and ultrapure water for three times after        ultrasonic treatment for 30 min; centrifugal separation was        performed to take the lower layer of solid; vacuum drying was        performed at 60° C. to obtain treated nanosilicon spheres; and        0.2 g of the treated nanosilicon spheres was uniformly dispersed        in 20 ml of a cyclohexane solution;    -   b. 1 g of citric acid and 0.03 g of histidine were uniformly        dissolved in 20 ml of ultrapure water under a heating condition        of a 50° C. water bath; pyrolysis was performed at 180° C. for 3        h to form a mixture; the mixture was filtered; a filtrate was        poured in a dialysis bag for dialysis treatment; and        freeze-drying was performed at −40° C. after the dialysis        treatment to obtain graphene quantum dots;    -   c. graphite oxide was prepared by a Hummer method; and the        concentration of a graphite oxide aqueous solution was 20 mg/ml.

Preparation Steps:

-   -   uniformly dissolving 0.006 g of the graphene quantum dots in 6        ml of ultrapure water, adding 0.85 ml of 0.3 mol/ml ZnCl₂        solution, and performing oscillation to generate a mixed        emulsifier;    -   mixing the obtained mixed emulsifier with 20 ml of the graphite        oxide aqueous solution with a concentration of 20 mg/ml and 20        ml of the cyclohexane solution containing 0.2 g of nanosilicon        spheres, and performing homogenization on the obtained mixture        for 30 s to form a uniform oil-in-water emulsion;    -   adding 1.2 g of hydrazine hydrate into the obtained emulsion in        three times for reduction, and performing a hydrothermal        reaction at 65° C. for 10 h to obtain a reduced emulsion; and    -   freeze-drying the obtained reduced emulsion under −40° C.,        performing washing with ethanol for three times, and performing        vacuum drying at 60° C. to obtain a carbon-silicon        three-dimensional structural composite material.

FIG. 1 is an SEM diagram of a carbon-silicon three-dimensionalstructural composite material prepared in Embodiment 2, in which picturea shows an overall morphology of the carbon-silicon composite material;and picture b shows a morphology of a surface, which is wrapped withgraphene, of the carbon-silicon composite material. As shown in picturea, the surface of the silicon sphere is wrapped with a layer ofsubstance; and the overall wrapped structure is uniform. The overallsize of the wrapped composite material is between 3 μm and 10 μm. Thesurface morphology of the object in picture b assists in verifying thewrapped structure of graphene on the surface of the material.

FIG. 2 shows comparison of electrode material specific capacities atdifferent current densities, in which, graph c shows an electrode madeof the carbon-silicon composite material prepared in Embodiment 2; andgraph d shows a pure silicon material electrode. As shown fromcomparison of curves, the specific capacity of the pure siliconelectrode decreases rapidly with the increase of the current densityunder different current densities, while the specific capacity of thecarbon-silicon composite material electrode obtained by the presentsolution decreases gently. Mechanical properties of the graphenematerial of the present solution can solve the problem of materialcracking due to volume expansion of silicon spheres, help reduce theloss of the high-capacity nanosilicon sphere material and improve cycleperformance of the electrode material. Meanwhile, the composite materialhas improved charge transport performance and ion diffusion ability ofthe silicon spheres, and has improved rate performance of the electrodematerial.

The above-mentioned specific implementations further explained thepurpose, technical solutions and beneficial effects of the presentdisclosure in detail. It should be understood that the above are onlyspecific implementations of the present disclosure, and are not intendedto limit the scope of protection of the present disclosure. Anymodifications, equivalent substitutions, improvements, etc. made withinthe ideas and principle of the present disclosure should be included inthe scope of protection of the present disclosure.

What is claimed is:
 1. A preparation method of a carbon-siliconthree-dimensional structural composite material, comprising thefollowing steps: a first step of dissolving 0.004 g to 0.006 g ofgraphene quantum dots in 4 ml to 6 ml of ultrapure water, dropwiseadding 0.65 ml to 0.85 ml of a CuCl₂ or ZnCl₂ solution having aconcentration of 0.2 mol/ml to 0.3 mol/ml, and performing oscillation togenerate a mixed emulsifier; a second step of mixing the mixedemulsifier obtained in the first step with 10 ml to 20 ml of a graphiteoxide aqueous solution having a concentration of 10 mg/ml to 20 mg/mland 10 ml to 20 ml of a cyclohexane solution containing 0.1 g to 0.2 gof nanosilicon spheres, and performing homogenization for 20 s to 30 sto form a uniform oil-in-water emulsion; a third step of adding 0.9 g to1.2 g of hydrazine hydrate into the emulsion obtained in the second stepfor reduction, and performing a hydrothermal reaction to obtain areduced emulsion; and a fourth step of freeze-drying the reducedemulsion obtained in the third step, performing washing with a washingliquid, and performing vacuum drying, to obtain the carbon-siliconthree-dimensional structural composite material.
 2. The preparationmethod of the carbon-silicon three-dimensional structural compositematerial according to claim 1, wherein the graphene quantum dots in thefirst step are prepared by: uniformly dissolving 1 g of citric acid and0.03 g of histidine in 20 ml of ultrapure water under a heatingcondition of a 40° C. to 50° C. water bath, performing pyrolysis at 180°C. for 3 h to form a mixture, filtering the mixture, pouring a filtratein a dialysis bag for dialysis treatment, and performing freeze-dryingat −40° C. after the dialysis treatment to obtain the graphene quantumdots.
 3. The preparation method of the carbon-silicon three-dimensionalstructural composite material according to claim 1, wherein the graphiteoxide in the second step is prepared by a Hummer method.
 4. Thepreparation method of the carbon-silicon three-dimensional structuralcomposite material according to claim 1, wherein the nanosilicon spheresin the second step have a particle diameter denoted by r, where rsatisfies 20 nm≤r≤120 nm.
 5. The preparation method of thecarbon-silicon three-dimensional structural composite material accordingto claim 1, wherein the cyclohexane solution containing the nanosiliconspheres in the second step is prepared by: adding the nanosiliconspheres into a mixed solution prepared by acetone, ethanol, and wateraccording to a ratio of 1:1:1, performing ultrasonic treatment for 30min, performing washing with ethanol and ultrapure water for three timesafter the ultrasonic treatment, performing centrifugal separation, andtaking a lower layer of solid, performing vacuum drying at 60° C. toobtain treated silicon spheres, and uniformly dispersing 0.1 g to 0.2 gof the treated nanosilicon spheres in 10 ml to 20 ml of a cyclohexanesolution.
 6. The preparation method of the carbon-siliconthree-dimensional structural composite material according to claim 1,wherein the hydrothermal reaction in the third step is performed at atemperature of 60° C. to 65° C. for 8 h to 10 h.
 7. The preparationmethod of the carbon-silicon three-dimensional structural compositematerial according to claim 1, wherein the freeze-drying in the fourthstep is performed at a temperature of −40° C.
 8. The preparation methodof the carbon-silicon three-dimensional structural composite materialaccording to claim 1, wherein the washing liquid in the fourth step isethanol.
 9. The preparation method of the carbon-siliconthree-dimensional structural composite material according to claim 1,wherein the vacuum drying in the fourth step is performed at atemperature of 60° C.